1. Field of the Invention
The present invention relates to an electric power steering apparatus for transmitting power from an electric motor, which serves as an assistive steering force (steering assisting force), to a vehicle steering system, in order to reduce the burden on the driver of a vehicle to operate a steering member such as a steering wheel when the driver turns the steering member to steer the vehicle.
2. Description of the Related Art
Recent years have seen widespread use of electric power steering apparatus, which detect a steering torque generated by the steering wheel of a vehicle with a steering torque sensor, and energize an electric motor to generate an assistive steering force depending on the detected steering torque, in order to allow the driver of the vehicle to turn the vehicle by applying a light steering force to the steering wheel.
Such electric power steering apparatus perform phase compensation on the steering torque that is detected by the steering torque sensor for achieving control stability.
Japanese Laid-Open Patent Publication No. 2004-098754 (hereinafter referred to as “JP2004-098754A”) discloses an electric power steering apparatus, which reduces the gain of a phase compensation and simultaneously performs a greater phase-lag compensation, i.e., a smaller phase-lead compensation, as the steering torque detected by a steering torque sensor becomes greater, and which reduces the gain and performs a greater phase-lag compensation, i.e., a smaller phase-lead compensation, as the vehicle speed becomes lower.